The present invention relates to a process for preparing novel polyolefins. More particularly, the present invention is concerned with a process for preparing polyolefins of good particles having a large average particle diameter and a narrow molecular weight distribution, which process is capable of greatly increasing the polymer yield per solid and that per transition metal, thereby permitting the omission of the step of removing catalyst remaining in the resulting polymer, further capable of increasing the bulk density of the polymer and decreasing a fine particulate portion of the polymer.
Heretofore, in this technical field there have been known many catalysts comprising inorganic magnesium solids as carriers such as magnesium halide, magnesium oxide and magnesium hydroxide and a transition metal compound such as a titanium compound or a vanadium compound supported on the carriers. However, the polyolefins obtained in the prior art are generally low in bulk density, relatively small in average particle diameter and generally wide in particle size distribution so contain a large proportion of fine particles. Besides, when these powdery polymers are subjected to forming, there arise problems such as dusting and lowering of the forming, efficiency. For the reason, improvement has keenly been desired from the standpoint of productivity and polymer handling. Further, still further improvements are considered necessary in order to satisfy the recent keen desire for omitting the pelletizing step and using a powdery polymer directly in a processing machine.
The present inventors have previously found out a novel catalyst component with the above drawbacks remedied and already filed patent applications thereon (see Japanese Patent Publication Nos. 11651/1989 and 12289/1989 and Japanese Patent Laid Open Nos. 149605/1985, 32105/1987 and 207306/1987). The use of this catalyst component can afford a polymer having a high bulk density and a large average particle diameter. However, a further improvement has been considered necessary for omitting the pelletizing step and using a powdery polymer directly in a processing machine.
The present inventors have also proposed a catalyst capable of affording a polymer having a narrow molecular weight distribution and a reduced proportion of low molecular weight components, which is required particularly in the film field, (see Japanese Patent Application No. 200348/1989). However, this polymer still cannot be considered satisfactory.
Having made extensive studies for the purpose of remedying such drawbacks and obtaining in an extremely high activity a polymer having a high bulk density, a narrow particle size distribution, an extremely small proportion of fine particles and a narrow molecular weight distribution, the present inventors accomplished the present invention.